1. Technical Field
The present invention relates to a fixing device and an image forming apparatus incorporating the same, and more particularly, to a fixing device that fixes a toner image in place on a recording medium with heat and pressure, and an electrophotographic image forming apparatus, such as a photocopier, facsimile machine, printer, plotter, or multifunctional machine incorporating several of these features, that incorporates the fixing device.
2. Background Art
In electrophotographic image forming apparatuses, such as photocopiers, facsimile machines, printers, plotters, or multifunctional machines incorporating several of these features, an image is formed by attracting developer or toner particles to a photoconductive surface for subsequent transfer to a recording medium such as a sheet of paper. After transfer, the imaging process is followed by a fixing process using a fixing device, which permanently fixes the toner image in place on the recording medium with heat and pressure.
In general, a fixing device employed in electrophotographic image formation includes a pair of generally cylindrical looped belts or rollers, one being heated for fusing toner (“fuser member”) and the other being pressed against the heated one (“pressure member”), which together form a heated area of contact called a fixing nip. As a recording medium bearing a toner image thereupon enters the fixing nip, the fuser member heats the recording medium to fuse and melt the toner particles, while the pressure member presses the recording medium against the fuser member to fix the molten toner onto the recording medium.
Various methods have been proposed to provide a fast, high-quality fixing process that can process a toner image with short warm-up time and first-print time without causing image defects even at high processing speeds.
For example, there is known a belt-based fixing device that employs a pair of opposed rotary members, one being a fuser belt looped into a generally cylindrical configuration, and the other being a generally cylindrical, rotatable pressure member, pressed against each other to form a fixing nip therebetween, through which a recording medium is conveyed under heat and pressure. The fixing device also includes a fuser pad inside the loop of the fuser belt to support pressure from the pressure member, which may be reinforced with a reinforcing member for protection against deformation or displacement under nip pressure.
According to this method, the fuser belt is equipped with a tubular piece of thermally conductive metal, or heat pipe, disposed inside the loop of the fuser belt for heating the fuser belt through conduction. The heat pipe has a heater disposed inside its tubular body, from which heat is imparted to the entire circumference of the fuser belt looped around the heat pipe.
Although generally successful in terms of start-up performance, the fixing device depicted above cannot meet ever-increasing requirements for accelerated warm-up time and first-print time while maintaining low power consumption, as is demanded of today's high-speed imaging equipment.